In traditional offset printing, a facsimile of the final document to be printed for the purpose of proofing may typically be created on a slow, high quality, low volume desktop device for customer approval. It is the intent of the offset press to match this proof. Such a proof is called a contract proof. Until recently, the resolution of the typical offset press greatly exceeded the resolution of most commercial “off the shelf” inkjet printers. Prior to the use of digital inkjet proofs, the contract proof may have been created using the exact film that would be used to image the plates for the offset run. By using similar ink, and similar media, the high quality proofing system could be made to match the offset press in both dot structure and color. The customer may sign the single copy produced by the proofer and attend the press run to make sure that the offset press output matched the proof prior to the start of mass production. Proof copies would typically not be created directly on the press due to the cost, waste, make-ready time and lost production time. The offset press is designed to make thousands or more copies while the high quality proofer would be optimized for creating just a single copy.
Present high quality inkjet proofers, on the order of 2400 or more dots per inch (dpi) have greatly reduced the time and expense involved in creating an offset proof. These high quality devices can now mimic the high quality achieved on an offset press. However, a digital press or high speed digital inkjet presses print at a resolution lower than the desktop inkjet proofing devices. A proof of the continuous tone data produced by one of these devices exceeds the quality and character of output achievable on the digital press.
In order to better mimic the output of the digital press and to allow the digital press to meet or exceed the quality found on these proofs, the apparent resolution of these desktop proofing devices must be lowered to match that of the digital press. This can be best accomplished on devices that have resolutions which are multiples of 300 dpi. Merely reducing the resolution of the data to 300 dpi will not reproduce the apparent graininess of the digital press. The continuous tone data will still be reproduced at the selected output resolution, resulting in an output which approximates photographic quality. In order to simulate the graininess of the digital press on these high quality devices, the continuous tone files must also be limited to the number of discrete colors that the digital press can reproduce.
It is seen, therefore, that it would be desirable to be able to separate the digital workflow from the color output, to more precisely match the proofing copy to the final print run.